let _Vue = null

export default class VueRouter {
    static install (Vue) {
        // 1. 判断当前插件是否已经被安装
        if (VueRouter.install.installed) {
            return
        }
        VueRouter.install.installed = true
        // 2. 把Vue构造函数记录到全局变量
        _Vue = Vue
        // 3. 把创建的Vue实例时传入的router对象注入到vue实例上
        _Vue.mixin({
            beforeCreate () {
                if (this.$options.router) {
                    _Vue.prototype.$router = this.$options.router
                    this.$options.router.init()
                }
            }
        })
    }

    constructor (options) {
        this.options = options
        this.routeMap = {}
        this.data = _Vue.observable({
            current: '/'
        })
    }

    createRouteMap () {
        // 将路由规则解析成键值对的形式存储在routeMap中
        this.options.routes.forEach(route => {
            this.routeMap[route.path] = route.component
        })
    }

    initComponents (Vue) {
        Vue.component('router-link', {
            props: {
                to: String
            },
            render (h) {
                return h('a', {
                    attrs: {
                        href: this.to
                    },
                    on: {
                        click: this.clickHandler
                    }
                }, [this.$slots.default])
            },
            methods: {
                clickHandler (e) {
                    // history模式
                    //history.pushState({}, '', this.to)
                    // hash模式
                    window.location.hash = '#' + this.to
                    this.$router.data.current = this.to
                    e.preventDefault()
                }
            }
            //template: '<a :href="to"><slot></slot></a>'
        })

        const self = this
        Vue.component('router-view', {
            render (h) {
                // 当前路由组件
                const component = self.routeMap[self.data.current]
                return h(component)
            }
        })
    }

    init () {
        this.createRouteMap()
        this.initComponents(_Vue)
        this.initEvent()
    }

    initEvent () {
        /* window.addEventListener('popstate', () => {
            this.data.current = window.location.pathname
        }) */
        window.addEventListener('load', this.hashChange.bind(this))
        window.addEventListener('hashchange', this.hashChange.bind(this)) 
    }

    hashChange () {
        if (!window.location.hash) {
            window.location.hash = '#/'
        }
        this.data.current = window.location.hash.substr(1)
    }
}
